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// To execute from the command line: `dotnet fsi fsharp/ch-2.fsx`
let task2 (d_and_i_s: string) =
// lo,hi will be modified via side-effects within .map
let mutable lo = -1
let mutable hi = 1 + d_and_i_s.Length
let squeeze_from_ends (di: char): int =
if di = 'D'
then hi <- hi - 1; hi
else lo <- lo + 1; lo
(d_and_i_s + "I")
|> Seq.map(squeeze_from_ends)
|> Seq.toList
// This is only used for extra round-trip testing.
let ints_to_DI (ns: list<int>) =
ns |> List.pairwise
|> List.map (fun (a, b) -> if a > b then "D" else "I")
|> List.reduce (+)
// Below this point is test harness and data
let mutable test_number = 0
let is (got: 'a) (expected: 'a) (test_name: string) =
test_number <- test_number + 1
let ok_msg = if (got = expected) then "ok" else "not ok"
printfn $"{ok_msg} {test_number} {test_name}"
()
type TestRecord = { di: string; expected: list<int> }
let tests : list<TestRecord> = [
{ di = "IDID" ; expected = [0; 4; 1; 3; 2] };
{ di = "III" ; expected = [0; 1; 2; 3] };
{ di = "DDI" ; expected = [3; 2; 0; 1] };
]
for test : TestRecord in tests do
let got: list<int> = task2 test.di
is got test.expected ("Task2 example: " + test.di)
is (ints_to_DI got) test.di ("Task2 example: " + test.di + " round-trip")
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